HELP WITH PORT CALCULATIONS

[HemiRick]

A buddy of mine built a infinite baffle sub w 2 of those Fi woofers he used the 18 in versions. They are AMAZING. Solid bass thats very natural and very little distortion. I haven't listened to them much w music yet, but for HT I haven't heard/felt anything better.

 

[dreadknot]

thanks for that im definitely considering one of ther 15in drivers

 

[A800]

Usually the simulated port length is too long.
To obtain the desired response there is no way around measurements.
If you have no measurement equipment use sine waves.
The tuning frequency is around the point where the speaker will barely move.

Also like already mentioned keep an eye on port velocity (12 m/s) and driver excursion.
Personally I like slot ports of reasonable width the most.
Keep the inner opening of the port in proximity of the speaker for the best sound.
Port flares help.
Good luck.

 

[dreadknot]

thank

 

[dreadknot]

my revised build concept

the three black wedges at the top, bottom an back are layered Acoustic Panels Soundproof Foam

 

[witwald]

I'd suggest that you try and add a fillet with a large radius to replace the sharp 90-degree angle in the port. That location looks ripe for generating quite a bit of turbulence, especially at higher SPLs when the port needs to be working hard.

 

[dreadknot]

you mean rounds to the corners in the port ,to the back two only or all 12 corners in the port an by how much .5 or .75 or by 1 in

an how do you think a epoxy resin coat to the interior of the cab an port will effect to sound

 

[witwald]

The back two were the ones that I was concerned about, where the vertical part of the port transitions to the horizontal part of the port. The radius would need to be quite large, say equal to the height of the port.

 

[dreadknot]

wouldn't that subtract from the required size of the port an interfer with the tuned fq

 

[witwald]

The radius can be accounted for in the length calculation. The sharp edge will interfere with the tuned frequency, as the turbulence will impede the flow and may affect the way that the mass of air in the port behaves, potentially making it behave less like the theoretical lumped mass that it is assumed to be.

 

[dreadknot]

does this sound right the rear wall of my port reads as 61.75in according to autocad measurments ,an as 61.75in in lenght is what winisd suggests based on a 2in port hight an 16.3in wide

is this correct

with the rounded corners as shown in my updated concept

if it is ive just got to figure out how to pull off such a cut

 

[witwald]

If you are summing over the length of the rear wall of the port to compute a nominal port length, then I believe that will give a slight overestimate of the port length. The length of the port might be better approximated by summing the length of the port through the centre of the vertical cross-section. That will be a little bit shorter than the length of the rear wall of the port. There is also an "end correction" that needs to be added to the physical length of the port. What does WinISD suggest will be the end correction? Does it include the end correction in its computations?

It would also be helpful if your drawings included dimensions, ideally in mm, although inches would suffice.

If you'd like to share your WinISD project file, I can take a look at the design of the low-frequency alignment to give me a better idea of what you're trying to achieve. I think you can attach files, if the button below this message is anything to go by.